This invention relates to optical transducers, and more particularly to optical transducers for determining liquid level.
Transducers for measuring liquid level are often used in vehicles, industrial equipment and other systems and components. The electrical output of such transducers change in response to a change in the liquid being measured, and is typically in the form of a change in resistance, capacitance, current flow, magnetic field, frequency, and so on. These types of transducers may include variable capacitors or resistors, optical components, Hall Effect sensors, strain gauges, ultrasonic devices, and so on.
By way of example, prior art liquid level sensors, such as fuel level sensors for motor vehicles, usually include a float that rides on an upper surface of the fuel in a fuel tank. The float is typically connected to one end of a pivot arm while the other end of the pivot arm includes a wiper mechanism that brushes against a resistor strip when the arm is rotated due to a change in fuel level in the tank. Such sensors are prone to wear, mechanical and/or electrical breakdown or, at the very least, inaccurate liquid level detection.
In an effort to overcome these drawbacks, liquid level transducers with no moving parts have been developed. Such sensors include heated wires or film with the liquid being measured functioning as a heat sink, variable capacitance devices with the measured liquid functioning as the dielectric, ultrasonic devices, optical devices, and Hall-Effect type devices. Many of these liquid level transducers suffer from one or more of the following drawbacks: the detection of liquid level may be inaccurate; fine wires can be affected by vibration and movement, such as with heated wire probes; fuel additives and contaminants can cause corrosion of various transducer components; the electrical output of the transducer may vary due to water or contaminants in the fuel, such as with capacitance-type probes; and such transducers may be cost-prohibitive in many transportation markets that require a low-cost solution.